Vesicular stomatitis virus and Newcastle disease virus are enveloped, RNA viruses which assemble at host cell plasma membrane. Mature virions are formed when regions of plasma membrane containing viral components bud from the cell. The project proposed is designed to explore some of the unresolved problems in the morphogenesis of these viruses. The goal of these studies is 1) to define the interactions of viral proteins in plasma membranes necessary for assembly and budding of the virus and 2) to characterize in detail the intracellular processing of viral glycoproteins. These studies include characterization of temperature sensitive mutants defective in assembly of virions.